1. Field of the Invention
The invention relates to an illumination device which provides an illumination beam which is essentially homogeneous in at least one cross-sectional direction, in particular for a laser scanning microscope, where an original beam which is inhomogeneous in cross-section, in particular Gaussian-shaped, is conducted to a converting unit which transmits the illumination beam.
2. Related Art
In many applications an illumination beam expanded in the form of a line is used, for example, for barcode scanners or for laser scanning microscopes sampling in the form of a row. One possibility for obtaining such a beam in the form of a line consists of a fast redirection of the laser beam along a row so that indeed at each point in time only one point of the row is illuminated, but averaged over a certain period of time a row is illuminated. Another approach which is also used in the state of the art to generate illumination beams shaped in the form of a line uses cylinder optics which anisotropically expand a beam bundle in a known manner. Such a cylinder-optical design is described as mirror optics, for example, in U.S. Pat. No. 4,589,738. There a beam is first directed onto a convex mirror not described in more detail and the beams diverging there are focused by means of a cylindrical lens onto a line.
Cylinder optics in principle does not change the beam profile. It merely expands it in a certain direction. A Gaussian-shaped beam, as is customarily transmitted by a laser beam source or a collimator for the light guide fiber bundle, therefore remains, even after treatment with a cylinder optics, Gaussian-shaped in profile, even if the width of the Gaussian shape after the cylinder optics is no longer the same in all direction transverse to the beam propagation. This has as a consequence the fact that the beam intensity varies sharply along a row or line. In applications which are sensitive with respect to this, one is aided by the fact that the beam is first expanded with a cylinder optics, where the expansion is very much greater than the width of the row or line later required and then, by means of screens, edge areas of the row or line in which the intensity of the radiation has dropped off too sharply with respect to the center are masked. Unfortunately, this has poor efficiency with regard to the utilization of the beam intensity originally generated.
U.S. Pat. No. 4,862,299 discloses a lens which expands a laser beam and, in so doing, re-forms the beam profile to be not Gaussian-shaped. In this document the lens is represented in numerous forms in cross-section and it causes an expansion to approximately rectangular beam shape. For application in laser scanning microscopy the approach of U.S. Pat. No. 4,862,299 is, however, unsuitable for chromatic reasons.